1,4-Diazoniabicyclo[2.2.2]octane tetrachloridocadmate(II) monohydrate

The asymmetric unit of the title compound (C6H14N2)[CdCl4]·H2O contained one 1,4-diazabicyclo[2.2.2]octane dication, a tetrahedral CdCl42−anion and a lattice water molecule. In the crystal, the solvate water molecule interacts with the cationic and anionic speciesviaN—H...O and O—H...Cl [O...Cl = 3.289 (7) Å] hydrogen-bond interactions, respectively, leading to a layered supramolecular structure extending parallel to (011).

catena-Poly[[diaquabis(μ3-5-carboxylato-1H-pyrazole-3-carboxylic acid-κ3O3:O3;O5)dilithium(I)] monohydrate]

The basic structural unit of the title polymeric ribbon, {[Li2(C5H3N2O2)2(H2O)2]·H2O}n, is a centrosymmetric dinuclear complex in which the two LiIions are bridged by two carboxylato O atoms, to generate a centrosymmetric Li2O2core. These are connected into a chain along [01-1] by carboxylic acid–carbonyl-O bonds. The tetrahedral coordination of the LiIcation is completed by an aqua ligand. The carboxylic acid is involved in an intra-ribbon hydrogen bond. A solvate water molecule showing positional (50:50) disorder is observed. Polymeric ribbons along [01-1] are connected by O—H...O, N—H...O and O—H...N hydrogen bonds into a three-dimensional architecture.

Tautomerism in 3{5}-(dimethoxyphenyl)pyrazoles

The single-crystal X-ray structures of 3{5}-(2′,5′-dimethoxyphenyl)pyrazole (HI) and the hemihydrate of 3 {5}-(3/,4′-dimethoxyphenyl)pyrazole (IV) have been determined. Compound (HI) exists purely as the 5-substituted prototropomer in the crystal; the pyrazole pyrollic N—H proton is involved in a three-way hydrogen bond, involving an intramolecular contact with a methoxy oxygen donor and an intermolecular interaction to the pyridinic N atom of a neighbouring molecule, forming discrete hydrogen-bonded dimers. There is no evidence of degenerate proton transfer within the dimeric units from CPMAS 13C NMR spectroscopy, in contrast to other known pyrazoles that associate in this manner. In (IV).1/2H2O, however, the pyrrolic proton is disordered over both N(1) and N(2) via hydrogen bonding to the solvate water molecule. CPMAS 13C NMR spectroscopy shows that the prototropic disorder in (IV).1/2H2O is static at temperatures up to 370 K. Solution 1H and 13C NMR data in DMSO-d 6 show that for both (HI) and (IV) the 3- and 5-substituted tautomeric forms are similarly populated in this solvent, suggesting both that the intramolecular hydrogen bond in (HI) has been disrupted and that the two tautomers of (HI) and (IV) are close in energy.